US20030129960A1 - Satellite broadcast receiving converter with lower power consumption - Google Patents

Abstract

A control portion detects the presence or absence of a pulse signal provided from a satellite broadcast receiver through a port PO to output a control signal PDOUT. In accordance with control signal PDOUT, a power supply circuit stops a supply of one of a power supply potential BIAS1fed to LNA22A and a power supply potential BIAS2fed to LNA22B. Therefore, the power consumption in an LNB designed for multi-satellite can be reduced and even a satellite broadcast receiver having a small current-supply capability can be connected. In this way, a low noise block down converter for multi-satellite with lower power consumption can be provided.

Description

BACKGROUND OF THE INVENTION
• 1. Field of the Invention[0001]
• The present invention relates to a satellite broadcast receiving converter, and more particularly to a Low Noise Block Down Converter (referred to as LNB hereinafter) receiving radio waves from a plurality of satellites for use in satellite broadcasting or satellite communication.[0002]
• 2. Description of the Background Art[0003]
• At present, broadcasting satellites (three satellites referred to as DBS[0004]1, DBS2, and DBS3) having a signal frequency band of a BSS (Broadcast Satellite Service) frequency band at 12.2-12.7 GHz are launched over the North America in the vicinity of the west longitude 101°. Two kinds of circularly polarized signals of right-hand circular polarization and left-hand circular polarization are used in the BSS frequency band as transmission signals from the satellite.
• FIG. 11 is a diagram illustrating RF (Radio Frequency) signals received from a plurality of satellites.[0005]
• Referring to FIG. 11, a satellite broadcasting receiving antenna receiving a satellite broadcasting signal transmitted from a[0006]satellite500 and asatellite502 includes areflector plate504 reflecting the satellite broadcasting signal transmitted from the two satellites, and an LNB506 amplifying the satellite broadcasting signal reflected atreflector plate504 with low noise and converting the frequency to a lower frequency band. LNB506 is connected to a satellite broadcast receiver such as a television receiver.
• A coaxial cable is normally used to receive radio waves at a satellite broadcasting antenna and to introduce the signal to an indoor BS tuner. The radio waves received at the antenna, however, cannot be introduced indoors directly with the coaxial cable.[0007]
• A metal tube called a waveguide has to be used to introduce the radio waves for satellite broadcasting having an extremely high frequency. The use of the waveguide requires a big hole to be provided on a wall to introduce a signal from the antenna to the indoor satellite broadcast receiver, and causes large attenuation, and therefore it is not realistic.[0008]
• Therefore, LNB[0009]506 installed at the antenna is used to lower the frequency of the received signal to such a frequency as to be introduced even through the coaxial cable and then to transmit the signal to the indoor satellite broadcast receiver. The indoor satellite broadcast receiver includes a scramble decoder, which allows descrambling for displaying an image on a display unit.
• The input portion of LNB[0010]506 is provided withfeed horns510A and510B corresponding tosatellites500 and502, respectively.
• Conventionally, an LNB designed for multi-satellite has been used in which the RF signals input from a plurality of satellites are switched by one LNB switch and selectively received. This LNB designed for multi-satellite receives the signal from each satellite through respective[0011]independent feed horns510A and510B. Therefore, the substrate havingfeed horns510A and510B connected is provided with a plurality of independent input portions. To amplify the broadcasting signal corresponding to each of the plurality of satellites that is supplied from these input portions at least one low noise amplifier circuit (LNA) is present for each satellite. In the signal processing after this LNA, a signal from a desired satellite is selected by switching.
• FIG. 12 is a schematic block diagram showing a first exemplary configuration of LNB for receiving transmission signals from a plurality of satellites in the conventional satellite broadcasting receiving system.[0012]
• Referring to FIG. 12, signals from[0013]satellites500 and502 are respectively received byfeed horns510A and510B.
• Two kinds of signals respectively received by[0014]feed horns510A and510B are amplified with low noise by LNA (Low Noise Amplifier)522A and522B.
• The RF signals amplified with low noise by LNA[0015]522A and522B are provided to the respective one inputs ofmixers530A and530B after unnecessary signals are removed through BPF (Band Pass Filter)528A and528B, respectively.
• The other inputs of[0016]mixers530A and530B respectively receive local oscillating signals fromlocal oscillator circuits526A and526B. The RF signals and the local oscillating signals are mixed inmixers530A and530B. As a result, the RF signals are converted to intermediate frequency (IF) signals in the intermediate frequency band.
• The IF signals from[0017]mixers530A and530B are respectively provided toPIN diodes532A and532B. WhenPIN diodes532A and532B are turned on, the IF signals are passed. On the other hand, when they are turned off, the IF signals are blocked. The selection of the IF signals is performed by the individual on/off control ofPIN diodes532A and532B.
• The selected IF signal is amplified by an[0018]IF amplifier534 and transmitted to a port PO through AC coupling using acapacitor535. The IF output signal is output from the port PO to a satellite broadcast receiver (not shown) for example a television receiver.
• FIG. 13 is a schematic block diagram showing a second exemplary configuration of the conventional LNB.[0019]
• Referring to FIG. 13, an LNB[0020]550 differs from LNB510 in thatPIN diodes532A and532B are not provided in the configuration of LNB510 illustrated in FIG. 12 andmixers530A and530B are directly connected toIF amplifier534.
• Furthermore, it differs from LNB[0021]510 in that apower supply circuit540 powers acircuit portion551 and acontrol portion552 and the power supplies for LNA522A and522B are independently controlled bycontrol portion552.
• The remaining configuration of LNB[0022]550 is similar to that of LNB510 and the description thereof will not be repeated.
• LNB[0023]550 selectively inputs a signal from the desired satellite toIF amplifier534 by turning off either of the power supplies for LNA522A and LNA522B.
• FIG. 14 is a diagram showing an exemplary configuration of receiving signals from a plurality of satellites where conventional LNB itself does not have a switching function.[0024]
• Referring to FIG. 14, three LNB[0025]1-LNB3 are provided for receiving radio waves from first to third satellites. A switch box SW-BOX receives the signals received at LNB1-LNB3 and selects any one of them.
• The selected signal is output from a port PO and input to a satellite broadcasting receiving device IRD (Integrated Receiver/Decoder) that is installed indoors.[0026]
• When a plurality of LNB corresponding to a plurality of satellites are internally mounted in one package in order to realize the LNB designed for multi-satellite, the following problems arise with only the switching selection of signals that are output from the internal LNB for each satellite as in the conventional circuit configuration.[0027]
• First of all, the satellite broadcast receiver that powers LNB has a limit in the current to be supplied. In order to allow a variety of conventional satellite broadcast receivers to be connected, even a satellite broadcast receiver having a small current capacity has to be handled. Although the provision of the switch box as shown in FIG. 14 allows the power to be supplied with a separate system, a compact LNB designed for multi-satellite cannot be implemented. Therefore, the power has to be supplied through a cable from the satellite broadcast receiver.[0028]
• In LNB[0029]510 shown in FIG. 12, the voltage applied from the satellite broadcast receiver through the port PO is converted into a prescribed power supply voltage bypower supply circuit540 and is supplied tocircuit portion511.
• In the configuration shown in FIG. 12, however, that LNA of two LNAs which amplifies the signal from the satellite that is not received is continuously supplied with power supply current from[0030]power supply circuit540, so that the power consumption of LNB is inevitably large.
• Second, as shown in FIG. 13, if the selection operation is performed by the on/off control of the power supplies for LNA, a noise caused in the mixer portion of the unselected LNA is unpreferably combined with the received signal from the selected satellite. Furthermore, there is a demand to transmit a received signal from one LNB to a plurality of satellite broadcast receivers. In this case, such a case cannot be handled in that a signal from a first satellite is sent to a first broadcast receiver and a signal from a second satellite is sent to a second broadcast receiver, for example.[0031]
SUMMARY OF THE INVENTION
• An object of the present invention is to provide an LNB with reduced noise in an output signal and with reduced current consumption.[0032]
• In accordance with one aspect of the present invention, a satellite broadcast receiving converter is provided that allows a first satellite broadcast receiver to receive broadcasting signals transmitted from a plurality of satellites. The converter includes a first signal receiving portion receiving a first broadcasting signal transmitted from a first satellite of a plurality of satellites to supply a first RF signal, a first amplifying portion amplifying the first RF signal, a second signal receiving portion receiving a second broadcasting signal transmitted from a second satellite of a plurality of satellites to supply a second RF signal, a second amplifying portion amplifying the second RF signal, a first frequency conversion portion converting outputs of the first and second amplifying portions respectively to first and second IF signals in an intermediate frequency band, selecting and outputting one of the first and second IF signals, a third amplifying portion amplifying an output of the first frequency conversion portion, a first port receiving a signal from the third amplifying portion for output to the first satellite broadcast receiver, a first DC component blocking portion provided between the third amplifying portion and the first port, a power supply circuit receiving a first external power supply potential from the first satellite broadcast receiver through the first port and independently supplying first and second internal power supply potentials respectively to the first and second amplifying portions, and a control portion instructing inactivation of an internal power supply potential, corresponding to an unselected satellite, of the first internal power supply potential and the second internal power supply potential to the power supply circuit in accordance with a select instruction applied from the first satellite broadcast receiver, and performing select control of the first frequency conversion portion.[0033]
• Therefore, the main advantage of the present invention is in that even a satellite broadcast receiver having a low power-supply capability can be connected since the power supply circuit selectively supplies the power supply potential to the amplifying portion and therefore the power consumption in the unused amplifying portion is reduced.[0034]
• Preferably, the power supply circuit includes a power supply potential generation portion receiving the first external power supply potential, a first switch circuit rendered conductive in accordance with an output of the control portion for outputting an output of the power supply potential generation portion as the first internal power supply potential, and a second switch circuit rendered conductive complimentarily to the first switch circuit for outputting the output of the power supply potential generation portion as the second internal power supply potential.[0035]
• Preferably, the satellite broadcast receiving converter includes a fourth amplifying portion amplifying an output of the first frequency conversion portion, a second port receiving a signal from the fourth amplifying portion for output to a second satellite broadcast receiver, and a second DC component blocking portion provided between the fourth amplifying portion and the second port. The first frequency conversion portion selects and outputs one of the first and second IF signals to the third amplifying portion in accordance with an output of the control portion, and selects and outputs one of the first and second IF signals to the fourth amplifying portion independently of selection for the third amplifying portion. The control portion includes a first detection portion detecting an instruction from the first satellite broadcast receiver, and a second detection portion detecting an instruction from the second satellite broadcast receiver. The power supply circuit includes a power supply potential generation portion receiving the first external power supply potential and a second external power supply potential provided from the second satellite broadcast receiver through the second port, a first switch circuit rendered conductive in accordance with an output of the first detection portion and an output of the second detection portion for outputting an output of the power supply potential generation portion as the first internal power supply potential, and a second switch circuit rendered conductive in accordance with the output of the first detection portion and the output of the second detection portion for outputting the output of the power supply potential generation portion as the second internal power supply potential.[0036]
• Therefore, another advantage of the present invention is in that a satellite broadcast receiving converter having a plurality of output terminals can be realized. Also in this case, the power supply to the unused amplifying portion is stopped and the power consumption is reduced, so that a satellite broadcast receiver having a small power-supply capacity can be connected.[0037]
• More preferably, the first switch circuit is rendered conductive when at least one of the output of the first detection portion and the output of the second detection portion indicates selection of the first satellite, and the first switch circuit is rendered non-conductive when neither of the output of the first detection portion and the output of the second detection portion indicates selection of the first satellite. The second switch circuit is rendered conductive when at least one of the output of the first detection portion and the output of the second detection portion indicates selection of the second satellite, and the second switch circuit is rendered nonconductive when neither of the output of the first detection portion and the output of the second detection portion indicates selection of the second satellite.[0038]
• More preferably, the instruction from the first satellite broadcast receiver to the first detection portion is provided through the first port as the presence or absence of a first pulse signal combined with the first external power supply potential. The instruction from the second satellite broadcast receiver to the second detection portion is provided through the second port as the presence or absence of a second pulse signal combined with the second external power supply potential. Both of the first and second pulse signals are signals indicative of selection of the first satellite. The power supply circuit further includes a first sense circuit sensing that the first external power supply potential is fed from the first satellite broadcast receiver to the first port, and a second sense circuit sensing that the second external power supply potential is fed from the second satellite broadcast receiver to the second port. The second switch circuit is rendered conductive in a first case where the first detection portion does not detect the first pulse signal and the first sense circuit senses that first external power supply potential is fed and in a second case where the second detection portion does not detect the second pulse signal and the second sense circuit senses that the second external power supply potential is fed, and the second switch circuit is rendered non-conductive in other cases.[0039]
• Therefore, the other advantage of the present invention is in that the total power consumption can be reduced even when a satellite broadcast receiver is not connected to one output port of the satellite broadcast receiving converter having a plurality of outputs.[0040]
• More preferably, the power supply circuit further includes a current distribution circuit receiving the first and second external power supply potentials respectively from the first and second ports and supplying operating power supply current to the power supply potential generation portion while preventing an unbalanced current supply from one of the first and second satellite broadcast receivers.[0041]
• Preferably, the control portion and the power supply circuit are accommodated in one IC package.[0042]
• Preferably, the satellite broadcast receiving converter includes a fourth amplifying portion receiving the first internal power supply potential as an operating power supply potential and amplifying a third RF signal receiving a third broadcasting signal transmitted from a third satellite of a plurality of satellites, a fifth amplifying portion receiving the second internal power supply potential as an operating power supply potential and amplifying a fourth RF signal receiving a fourth broadcasting signal transmitted from a fourth satellite of a plurality of satellites, a second frequency conversion portion converting outputs of the third and fourth amplifying portions respectively to third and fourth IF signals in an intermediate frequency band, selecting and outputting one of the third and fourth IF signals, a sixth amplifying portion amplifying an output of the second frequency conversion portion, a second port receiving a signal from the sixth amplifying portion for output to a second satellite broadcast receiver, and a second DC component blocking portion provided between the sixth amplifying portion and the second port. The control portion includes a first detection portion detecting an instruction from the first satellite broadcast receiver, and a second detection portion detecting an instruction from the second satellite broadcast receiver. The power supply circuit includes a power supply potential generation portion receiving the first external power supply potential and a second external power supply potential provided from the second satellite broadcast receiver through the second port, a first switch circuit rendered conductive in accordance with an output of the first detection portion and an output of the second detection portion for outputting an output of the power supply potential generation portion as the first internal power supply potential, and a second switch circuit rendered conductive in accordance with the output of the first detection portion and the output of the second detection portion for outputting the output of the power supply potential generation portion as the second internal power supply potential.[0043]
• Therefore, the other advantage of the present invention is in that the power consumption can be reduced even when signals are received from two or more satellites.[0044]
• The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.[0045]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic block diagram showing an entire configuration of an[0046]LNB1 of the present invention.
• FIG. 2 is a circuit diagram showing a configuration of a power supply circuit and[0047]periphery portion2 in accordance with a first embodiment.
• FIG. 3 is a circuit diagram showing a schematic configuration of a[0048]block39 in FIG. 2.
• FIG. 4 is a circuit diagram showing a configuration of a power supply circuit and[0049]periphery portion3 of LNB in accordance with a second embodiment.
• FIG. 5 is a circuit diagram showing a configuration of a[0050]block39A in FIG. 4.
• FIG. 6 is a circuit diagram showing a configuration of a power supply circuit and[0051]periphery portion4 of LNB in accordance with a third embodiment.
• FIG. 7 is a circuit diagram showing a configuration of a power supply circuit and[0052]periphery portion5 used in LNB in accordance with a fourth embodiment.
• FIG. 8 is a circuit diagram showing a configuration of a[0053]current distribution circuit170.
• FIG. 9 is a diagram illustrating a power supply circuit and[0054]periphery portion6 used in LNB in accordance with a fifth embodiment.
• FIG. 10 is a diagram illustrating a power supply circuit and periphery portion[0055]7 in accordance with a sixth embodiment.
• FIG. 11 is a diagram illustrating RF signals received from a plurality of satellites.[0056]
• FIG. 12 is a schematic block diagram showing a first exemplary configuration of LNB for receiving transmission signals from a plurality of satellites in a conventional satellite broadcasting receiving system.[0057]
• FIG. 13 is a schematic block diagram showing a second exemplary configuration of the conventional LNB.[0058]
• FIG. 14 is a diagram showing an exemplary configuration of receiving signals from a plurality of satellites where LNB itself does not have a switching function.[0059]
DESCRIPTION OF THE PREFERRED EMBODIMENTS
• In the following, the embodiments of the present invention will be described in detail with reference to the figures. It is noted that in the figures the same reference characters designate the same or corresponding parts.[0060]
• (First Embodiment)[0061]
• FIG. 1 is a schematic block diagram showing an entire configuration of an[0062]LNB1 in the present invention.
• Referring to FIG. 1, in the BSS frequency band, two kinds of circularly polarized signals of right-hand circular polarization and left-hand circular polarization are used as transmission signals from satellites.[0063]LNB1 includes afeed horn10A receiving two kinds of circularly polarized signals from a first satellite, that is, a right-hand circular polarization signal R1 and a left-hand circular polarization signal L1.
• The two kinds of circularly polarized signals L[0064]1 and R1 received byfeed horn10A are converted into linearly polarized signals by a phase shifter (not shown) of the feed horn portion and are output as RF signals L1 and R1 in the BSS radio frequency band.
• [0065]LNB1 further includes afeed horn10B receiving two kinds of circularly polarized signals from a second satellite, that is, a right-hand circular polarization signal R2 and a left-hand circular polarization signal L2.
• The two kinds of circularly polarized signals L[0066]2 and R2 received byfeed horn10B are converted into linearly polarized signals by a phase shifter (not shown) of the feed horn portion and are output as RF signals L2 and R2 in the BSS radio frequency band.
• RF signals L[0067]1 and R1 in the BSS radio frequency band that are converted into the linearly polarized signals are amplified by anLNA22A with low noise. Similarly, RF signals L2 and R2 are amplified by anLNA22B with low noise.
• [0068]LNA22A and22B are respectively supplied with power supply potentials BIAS1 and BIAS2 from apower supply circuit40. RF signals R1 and L1 amplified byLNA22A are applied to the respective one inputs ofmixers30A and30B after unnecessary signals are removed by bandpass filters (BPF)28A and28B. The respective other inputs ofmixers30A and30B receive local oscillating signals fromlocal oscillator circuit26A for respectively mixing with RF signals R1 and L1.
• As a result, RF signals R[0069]1 and L1 in the BSS frequency band are converted into IF signals in the intermediate frequency band and are respectively amplified byIF amplifiers37A and37B. IFamplifiers37A and37B respectively output IF signals R1A and L1A to switch IC32.
• RF signals R[0070]2 and L2 amplified byLNA22B are applied to the respective one inputs ofmixers30C and30D after unnecessary signals are removed respectively by bandpass filters (BPF)28C and28D. The respective other inputs ofmixers30C and30D receive local oscillating signals from alocal oscillator circuit26B for respectively mixing with RF signals R2 and L2.
• As a result, RF signals R[0071]2 and L2 in the BSS frequency band are converted into IF signals in the intermediate frequency band and are respectively amplified byIF amplifiers37C and37D. IFamplifiers37C and37D respectively output IF signals R2A and L2A to switch IC32.
• [0072]Switch IC32 selects an input signal in accordance with a pulse determination output signal PDOUT provided from acontrol portion38. The selected signal is amplified by anIF amplifier34, and is output as an IF output signal to a satellite broadcast receiver, for example a television receiver from a corresponding port PO after a low frequency noise being cut by acapacitor35.
• Meanwhile, LNB[0073]1 receives a DC voltage from a satellite broadcast receiver (not shown) through the port PO and a low frequency pulse signal at a few tens or kilohertz combined therewith. This DC voltage is cut down bycapacitor35 so as not to affect the IF amplifier. On the other hand, this DC voltage is applied to controlportion38 andpower supply circuit40.
• [0074]Control portion38 outputs pulse determination output signal PDOUT in accordance with the presence or absence of the low frequency pulse signal from the satellite broadcast receiver that is combined with the DC voltage.Power supply circuit40 controls power supply potentials BIAS1, BIAS2, BIAS0 in accordance with pulse determination output signal PDOUT.
• [0075]Control portion38 selects the left-hand polarization/the right-hand polarization depending on a high voltage or a low voltage (18V/13V) of the DC voltage from the satellite broadcast receiver through port PO. Furthermore,control portion38 selects the satellite depending on whether a pulse wave having an amplitude voltage of 0.6V at 22 kilohertz is combined or not. In this way, one of the total four kinds of IF signals can be designated and selected.
• [0076]Such switch IC32 to select one output signal from four input signals in accordance with a control signal is commercially available now. In the present invention, this control signal fromcontrol portion38 is also used in controlling the supply of power supply potential inpower supply circuit40.
• FIG. 2 is a circuit diagram showing the configuration of a power supply circuit and[0077]periphery portion2 in accordance with the first embodiment. It is noted that for the sake of simplicity the switching of two satellites depending on whether the pulse signal is combined as the control signal will be described.
• Referring to FIG. 2, the pulse signal combined with the DC voltage from port PO is applied to block[0078]39 as a pulse signal input PULIN through acapacitor42.Block39 includes a switch control portion and a switch IC.
• [0079]Block39 determines whether this pulse signal input PULIN includes a pulse signal, selects one of a system from the first satellite that receives RF signal R1 or L1 and a system from the second satellite that receives RF signal R2 or L2, and provides a signal SOUT toIF amplifier34.
• The signal amplified by[0080]IF amplifier34 is output throughcapacitor35 from port PO to the satellite broadcast receiver. The presence or absence of the pulse as determined inblock39 is provided topower supply circuit40 as pulse determination output signal PDOUT.
• [0081]Power supply circuit40 includes acapacitor62 absorbing a noise component of a DC potential receiving from PO, apower supply60 receiving the DC voltage from port PO for outputting a stabilized internal power supply potential IBIAS, acapacitor64 for stabilizing internal power supply potential IBIAS output frompower supply60, aswitch circuit52 outputting internal power supply potential IBIAS as power supply potential BIAS1 in accordance with pulse determination output signal PDOUT, and aswitch circuit54 outputting power supply potential IBIAS as a power supply potential BIAS2 in accordance with pulse determination output signal PDOUT.
• [0082]Power supply circuit40 further includes acapacitor82 absorbing a noise component of the DC voltage receiving from port PO, apower supply80 stabilizing and supplying the DC potential receiving from port PO for drivingswitch circuit54, and acapacitor84 stabilizing the output ofpower supply80.
• A triple-terminal regulator, for example, can be used as[0083]power supplies60 and80 outputting the stabilized DC voltage.
• [0084]Switch circuit52 includes adiode66 receiving at its anode pulse determination output signal PDOUT, aresistor68 having its one end connected to the cathode ofdiode66, aresistor70 connected between the other end ofresistor68 and a ground node, and anNPN transistor72 having its base connected to the other end ofresistor68 and having its emitter connected to the ground node.
• [0085]Switch circuit52 further includes aresistor74 having its one end connected to the collector ofNPN transistor72, aresistor76 connected between a node receiving power supply potential IBIAS and the other end ofresistor74, and aPNP transistor78 receiving at its emitter power supply potential IBIAS, having its base connected to the other end ofresistor74, and outputting power supply potential BIAS1 from its collector.
• [0086]Switch circuit54 includes aresistor88 receiving pulse determination output signal PDOUT at its one end, aresistor90 connected between the other end ofresistor88 and the ground node, and anNPN transistor92 having its base connected to the other end ofresistor88 and having its collector connected to the ground node.
• [0087]Switch circuit54 further includes adiode86 receiving at its anode the power supply potential output frompower supply80, adiode94 having its anode connected to the cathode ofdiode86, aresistor96 having its one end connected to the cathode ofdiode94, aresistor98 connected between the other end ofresistor96 and the ground node, and anNPN transistor100 having its base connected to the other end ofresistor96 and having its emitter connected to the ground node. The collector ofNPN transistor92 is connected to the cathode ofdiode86.
• [0088]Switch circuit54 further includesresistor102 having its one end connected to the collector ofNPN transistor100, aresistor104 connected between the other end ofresistor102 and a node receiving power supply potential IBIAS, and aPNP transistor106 having its emitter connected to the node receiving power supply potential IBIAS, having its base connected to the other end ofresistor102, and outputting power supply potential BIAS2 from its collector.
• FIG. 3 is a circuit diagram showing the schematic configuration of[0089]block39 in FIG. 2.
• Referring to FIG. 3, block[0090]39 includescontrol portion38 and switchIC32.
• [0091]Control portion38 includes apulse detection portion110 receiving a pulse input signal PULIN to detect the presence or absence of pulse signal at 22 kilohertz.Pulse detection portion110outputs 5V as pulse determination output signal PDOUT if a pulse is detected. On the other hand,pulse detection portion110outputs 0V as pulse determination output signal PDOUT if a pulse is not detected in pulse signal input PULIN.
• [0092]Switch IC32 includes aninverter112 receiving and inverting pulse determination output signal PDOUT, aswitch114 rendered conductive to output RF signal R1A, L1A as output signal SOUT if the level of pulse determination output signal PDOUT is 5V, and aswitch116 rendered conductive complimentarily to switch114 in response to the output ofinverter112 to output RF signal R2A, L2A as output signal SOUT.
• The operation of[0093]power supply circuit40 will now be described. As the pulse signal of 22 kilohertz is provided combined with the DC voltage from the satellite broadcast receiver (not shown), this pulse is applied to the input ofpulse detection portion110. As a result,pulse detection portion110 sets determination output signal PDOUT to 5V.
• Returning to FIG. 2, if the level of pulse determination output signal PDOUT is 5V,[0094]switch circuit52 outputs internal power supply potential IBIAS as power supply potential BIAS1. More specifically, when 5V is applied as pulse determination output signal PDOUT, current flows inresistors68 and70 throughdiode66 to raise the base potential ofNPN transistor72. As the collector-emitter ofNPN transistor72 is responsively rendered conductive, current flows throughresistors76 and74, and the potential difference between emitter and base ofPNP transistor78 is increased to render the collector-emitter ofPNP transistor78 conductive. Therefore, internal power supply potential IBIAS is output fromswitch circuit52 as power supplypotential BIAS1 throughPNP transistor78. This power supply potential BIAS1 is fed toLNA22A in FIG. 1.
• On the other hand,[0095]switch circuit54 does not output internal power supply potential IBIAS if pulse determination output signal PDOUT is 5V. More specifically, if pulse determination output signal PDOUT is 5V, current flows inresistors88 and90, so that the base potential ofNPN transistor92 rises and the collector-emitter ofNPN transistor92 is rendered conductive. Therefore, since the anode ofdiode94 is coupled to the ground node, current does not flow inresistors96 and98. Therefore, the collector-emitter ofNPN transistor100 is rendered non-conductive. Then, as current does not flow inresistors104 and102, no potential difference occurs between base and emitter ofPNP transistor106. Therefore, the collector-emitter ofPNP transistor106 is rendered non-conductive.
• In this case,[0096]LNA22B in FIG. 1 is not supplied with the power supply potential.
• The DC voltage from the satellite broadcast receiver that is not combined with the pulse signal will now be described. In this case, a pulse is not input to pulse input signal PULIN. Therefore[0097]pulse detection portion110 sets the level of pulse determination output signal PDOUT to 0V.
• In this case,[0098]switch circuit52 does not supply the power supply potential. More specifically, when the level of pulse determination output signal PDOUT is 0V, current does not flow inresistors68 and70. Therefore, since no potential difference occurs between base and emitter ofNPN transistor72, the collector-emitter ofNPN transistor72 is rendered non-conductive. In this case, current does not flow also inresistors76 and74, so that no potential difference occurs between base and emitter ofPNP transistors78. Therefore, the collector-emitter ofPNP transistor78 is rendered non-conductive.
• On the other hand,[0099]switch circuit54 supplies the power supply potential toLNA22B. More specifically, if the level of pulse determination output signal PDOUT is 0V, no current flows inresistors88 and90 so that the collector-emitter ofNPN transistor92 is rendered non-conductive.
• Then the current from[0100]power supply80 flows intoresistors96 and98 throughdiodes86 and94. Therefore, a potential difference occurs between base and emitter ofNPN transistor100, and the collector-emitter ofNPN transistor100 is rendered conductive. In this case, as current flows inresistors104 and102, a potential difference occurs between base and emitter ofPNP transistor106, and the collector-emitter ofPNP transistor106 is rendered conductive.
• As described above, LNB in accordance with the first embodiment uses[0101]power supply circuit40 to selectively supply the power supply potential toLNA22A orLNA22B. Therefore, the consumption power in the unused LNA is reduced so that even a satellite broadcast receiver having a low current-supply capability can be connected. Furthermore, because of the use of switch IC, the noise can be blocked from the circuitry receiving signals from the unselected satellite.
• (Second Embodiment)[0102]
• In the case where a plurality of satellite broadcast receivers are provided in a household, such an LNB that allows a plurality of satellite broadcast receivers to be connected is required.[0103]
• FIG. 4 is a circuit diagram showing a configuration of a power supply circuit and[0104]periphery portion3 of LNB in accordance with a second embodiment.
• Referring to FIG. 4, a[0105]block39A including a control portion and a switch IC can output two output signals SOUT1 and SOUT2. Output signal SOUT1 is amplified by an IFamplifier34A and applied to a first satellite broadcast receiver (not shown) from a port P01 through acapacitor35A. Output signal SOUT2 is amplified by an IFamplifier34B, is output from a port PO2 through acapacitor35B, and is provided to a second satellite broadcast receiver (not shown).
• A pulse input signal from the first satellite broadcast receiver is provided to block[0106]39A as a pulseinput signal PULIN1 through acapacitor42A. A pulse signal from the second satellite broadcast receiver is provided as a pulseinput signal PULIN2 from port PO2 through acapacitor42B to block39A.
• When a pulse is detected in pulse[0107]input signal PULIN1, block39A responsively decides the level of pulse determination output signal PDOUT1. It also decides the level of pulse determination output signal PDOUT2 in accordance with pulseinput signal PULIN2.
• [0108]Power supply circuit40A receives the supply of the DC voltage from ports PO1 and PO2, and outputs power supply potentials BIAS1 and BIAS2 toLNA22A andLNA22B, respectively, in accordance with pulse determination signals PDOUT1 and PDOUT2.
• [0109]Power supply circuit40A includes, in addition to the configuration ofpower supply circuit40 shown in FIG. 2, alow pass filter136 receiving and providing the DC voltage from port PO1 topower supply60 with the signal component being cut, and alow pass filter138 receiving and providing the DC voltage from port PO2 topower supply60 with the signal component being cut.Low pass filter136,138 is configured by inserting an inductance and a bypass condenser using a substrate pattern between the signal line and the power supply line, though not shown. These low pass filters prevent the mixing ofsignal SOUT1 and signalSOUT2.
• [0110]Power supply circuit40A further includes aswitch circuit52A in place ofswitch circuit52 and aswitch circuit54A in place ofswitch circuit54 in the configuration ofpower supply circuit40 shown in FIG. 2. The remaining configuration ofpower supply circuit40A is similar to that ofpower supply circuit40 and the description thereof will not be repeated.
• [0111]Switch circuit52A further includes adiode122 receiving pulse determination output signal PDOUT2 at its anode and having its cathode connected to the cathode ofdiode66, in the configuration ofswitch circuit52 shown in FIG. 2.
• [0112]Switch circuit52A also receives pulse determination output signal PDOUT1 at the anode ofdiode66 in the configuration ofswitch circuit52 shown in FIG. 2.
• The remaining configuration of[0113]switch circuit52A is similar to that ofswitch circuit52 and the description thereof will not be repeated.
• [0114]Switch circuit54A further includes, in addition to the configuration ofswitch circuit54 in FIG. 2, aresistor128 receiving pulse determination output signal PDOUT2 at its one end, aresistor130 connected between the other end ofresistor128 and the ground node, anNPN transistor132 having its base connected to the other end ofresistor128 and having its emitter connected to the ground node, adiode126 receiving the output potential frompower supply80 at its anode and having its cathode connected to the collector ofNPN transistor132, and adiode134 having its anode connected to the cathode ofdiode126 and having its cathode connected to the cathode ofdiode94.
• Furthermore,[0115]switch circuit54A differs fromswitch circuit54 in the configuration ofswitch circuit54 in FIG. 2, in that the other end ofresistor88 receives pulse determination output signal PDOUT1.
• The remaining configuration of[0116]switch circuit54A is similar to that ofswitch circuit54 and the description thereof will not be repeated.
• FIG. 5 is a circuit diagram showing the configuration of[0117]block39A in FIG. 4.
• Referring to FIG. 5, block[0118]39A includes acontrol portion38A and aswitch IC32A.
• [0119]Control portion38A includes apulse detection portion142A receiving pulseinput signal PULIN1 and detecting the presence or absence of the pulse of 22 kilohertz to output pulse determination output signal PDOUT1, and apulse detection portion142B detecting the presence or absence of the pulse of 22 kilohertz in pulseinput signal PULIN2 to output pulse determination output signal PDOUT2.
• [0120]Pulse detection portions142A and142B respectivelyoutput 5V as pulse determination output signals PDOUT1 and PDOUT2 when they detect the pulse. On the other hand,pulse detection portions142A and142B respectivelyoutput 0V as pulse determination output signals PDOUT1 and PDOUT2 when a pulse is not detected in the pulse input.
• [0121]Switch IC32A includesswitch circuits144A and144B.
• [0122]Switch circuit144A differs fromswitch IC32 shown in FIG. 3 in that it receives PDOUT1 in place of pulse determination output signal PDOUT and outputs output signal SOUT1 in place of output signal SOUT. The internal configuration, however, is similar to that ofswitch IC32 and the description thereof will not be repeated.
• [0123]Switch circuit144B differs fromswitch IC32 shown in FIG. 3 in that it receives PDOUT2 in place of pulse determination output signal PDOUT and outputsoutput signal SOUT2 in place of output signal SOUT. The internal configuration, however, is similar to that ofswitch IC32 and the description thereof will not be repeated.
• Returning to FIG. 4, the operation will be described briefly.[0124]
• Current flows in[0125]resistors68 and70 if the level of either of pulse determination output signals PDOUT1 and PDOUT2 is 5V or the level of both is 5V. Then, the collector-emitter ofNPN transistor72 is rendered conductive, and the collector-emitter ofPNP transistor78 is also rendered conductive responsively. Therefore BIAS1 is supplied toLNA22A. In the other case, that is, if the level of both pulse determination output signals PDOUT1 and PDOUT2 is 0V, power supply potential BIAS1 is not fed.
• In[0126]switch circuit54A, if the level of pulse determination output signal PDOUT1 is 0V or if the level of pulse determination output signal PDOUT2 is 0V, one or both of each collector-emitter ofNPN transistors92 and132 is/are rendered non-conductive. In either case, the base potential ofNPN transistor100 rises and the collector-emitter ofNPN transistor100 is rendered conductive. Responsively, the collector-emitter ofPNP transistor106 is rendered conductive and power supply potential BIAS2 is fed toLNA22B. In the other case, that is, if the level of both pulse determination output signals PDOUT1 and PDOUT2 is 5V, power supply potential BIAS2 is not fed.
• In this way, LNB having a plurality of output terminals can be realized with the use of the power supply circuit in accordance with the second embodiment. Also in this case, the power supply to the unused LNA is stopped and the power consumption is reduced, so that a satellite broadcast receiver having a small current-supply capacity can be connected.[0127]
• (Third Embodiment)[0128]
• FIG. 6 is a circuit diagram showing a configuration of a power supply circuit and[0129]periphery portion4 of LNB in accordance with a third embodiment.
• Referring to FIG. 6, although the power supply circuit and[0130]periphery portion4 is shown withblock39A being separated into two blocks of39B and39C, for the sake of illustration, in the circuit configuration shown in FIG. 4, the internal configuration is similar to that ofblock39A and the description thereof will not be repeated.
• In the circuit configuration in FIG. 6, power supply potentials BIAS[0131]1 and BIAS2 are output from apower supply circuit40B to two LNAs.
• [0132]Power supply circuit40B differs from the configuration ofpower supply circuit40A in that it includescapacitors152,154,162 and164,power supplies150 and160, anddiodes156 and166 in place of low pass filters136 and138,capacitors82 and84, andpower supply80 in the configuration ofpower supply circuit40A shown in FIG. 4. The configuration of the remaining part ofpower supply circuit40B is similar to that ofpower supply circuit40A and the description thereof will not be repeated.
• [0133]Capacitor152 absorbs the noise component of the DC voltage provided from portPO1. Power supply150 receives the DC voltage from port PO1 and outputs the stabilized DC voltage.Capacitor154 absorbs the noise caused in the output ofpower supply150. The DC voltage generated bypower supply150 is applied to the anode ofdiode86.
• [0134]Capacitor162 absorbs the noise component of the DC voltage applied from portPO2. Power supply160 receives the DC voltage from port PO2 and outputs the stabilized DC voltage.Capacitor164 absorbs the noise caused in the output ofpower supply160. The DC voltage generated bypower supply160 is applied to the anode ofdiode126.
• The DC voltage generated by[0135]power supply150 is fed topower supply60 throughdiode156. The DC voltage generated bypower supply160 is fed topower supply60 throughdiode166.
• In the configuration shown in FIG. 4, even when a satellite broadcast receiver is not connected to either port PO[0136]1 or PO2, the potentials of the collectors ofNPN transistors92 and132 rise, so that both of power supply potentials BIAS1 and BIAS2 may be activated.
• For example, consider a case where a satellite broadcast receiver is not connected to port PO[0137]2 and a pulse input is provided to port PO1. Since port PO2 is not connected to a satellite broadcast receiver, the level of pulse determination output signal PDOUT2 is 0V. On the other hand, since port PO1 is connected to a satellite broadcast receiver and receives a pulse input, the level of pulse determination output signal PDOUT1 is 5V.
• The combination of these pulse determination output signals PDOUT[0138]1 and PDOUT2 is the same with the case where a satellite broadcast receiver connected to port PO1 selects a first satellite and a satellite broadcast receiver connected to port PO2 selects a second satellite. Therefore, although only one satellite broadcast receiver is connected, both of two power supply potentials BIAS1 and BIAS2 are activated and two LNAs are operated.
• The operating power supply potential corresponding to two LNAs is fed from one satellite broadcast receiver, so that a problem will arise when the current-supply capability is limited.[0139]
• On the contrary, in the circuit configuration in accordance with the third embodiment shown in FIG. 6, when a satellite broadcast receiver is not connected to port PO[0140]2, for example,power supply160 does not output the power supply potential and therefore the anode ofdiode126 is at 0V. Therefore, even when pulse determination output signal PDOUT2 is 0V, the power supply potential BIAS2 is not activated as long as pulse determination output signal PDOUT1 is 5V.
• Similarly, when a satellite broadcast receiver is not connected to port PO[0141]1,power supply150 does not output the power supply potential and therefore the anode ofdiode86 is at 0V. Therefore, even when pulse determination output signal PDOUT1 is 0V, the power supply potential BIAS2 is not activated as long as pulse determination output signal PDOUT2 is 5V.
• Therefore, even if the current-supply capability of the satellite broadcast receiver connected to one port is limited, an LNB designed for multi-satellite can be used without problems.[0142]
• As described above, by employing the configuration of the power supply circuit illustrated in the third embodiment, the total power consumption can be reduced even when a satellite broadcast receiver is not connected to one port of LNB having a plurality of outputs.[0143]
• (Fourth Embodiment)[0144]
• In the configuration shown in FIG. 6, if the DC voltage output from[0145]power supply150 is higher than the DC voltage output frompower supply160, current is supplied only throughdiode156 and the potential difference between both ends ofdiode166 becomes smaller than the forward on voltage so that current does not flow indiode166. Therefore, the power supply current is fed only from the satellite broadcast receiver connected to port PO1. This is not preferable when the current-supply capability is limited, since the current borne by one satellite broadcast receiver becomes heavy.
• FIG. 7 is a circuit diagram showing a configuration of a power supply circuit and[0146]periphery portion5 for use in LNB in accordance with a fourth embodiment.
• Referring to FIG. 7, the power supply circuit and[0147]periphery portion5 includespower supply circuit40C in place ofpower supply circuit40B in the circuit configuration shown in FIG. 6.
• [0148]Power supply circuit40C includes acurrent distribution circuit170 in addition to the configuration ofpower supply circuit40B in FIG. 6. The cathode ofdiode156 is not directly connected topower supply60 but is connected tocurrent distribution circuit170. In the same manner, the cathode ofdiode166 is not directly applied topower supply60 but is connected tocurrent distribution circuit170.
• FIG. 8 is a circuit diagram showing the configuration of[0149]current distribution circuit170.
• Referring to FIG. 8,[0150]current distribution circuit170 includesresistors174 and176 connected in series between the ground node and the cathode ofdiode156 receiving at its anode a power supply potential VCC1 output frompower supply150, anNPN transistor172 having its collector connected to the cathode ofdiode156 and having its base connected to the connection node ofresistors174 and176, and aresistor178 having its one end connected to the emitter ofNPN transistor172.
• [0151]Current distribution circuit170 further includesresistors184 and186 connected in series between the ground node and the cathode ofdiode166 receiving at its anode a power supply potential VCC2 output frompower supply160, anNPN transistor182 having its collector connected to the cathode ofdiode166 and having its base connected to the connection node ofresistors184 and186, and aresistor188 having its one end connected to the emitter ofNPN transistor182.
• The other end of[0152]resistor178 and the other end ofresistor188 are connected, from which connection node current lout is fed topower supply60 in FIG. 7. Both of the resistance values ofresistors178 and188 are R1. Both of the resistance values ofresistors174 and184 are R2. Both of the resistance values ofresistors176 and186 are R3.
• The operation of[0153]current distribution circuit170 will be described briefly.
• The base potential of[0154]transistor172 can be obtained in the following equation (1). It is noted that VF is the forward voltage of the diode.
• VB=(VCC1−VF)×R3/(R2+R3)  (1)
• The emitter potential of[0155]transistor172 can be obtained in the following equation (2) in a simple manner. It is noted that VBE is the base-emitter voltage necessary to turn on the transistor.
• VE=(VCC1−VF)×R3/(R2+R3)−VBE  (2)
• Therefore current i[0156]1 flowing inresistor178 can be obtained in the following equation (3) by dividing the potential difference (VE−Vout) by resistance value R1.
• i1=[(VCC1−VF)×R3/(R2+R3)−VBE−Vout]/R1  (3)
• In a similar manner, at the side of[0157]transistor182, current i2 flowing inresistor188 can be obtained in the following equation (4).
• i2=[(VCC2−VF)×R3/(R2+R3)−VBE−Vout]/R1  (4)
• Therefore, current will not be fed only from one of power supplies and the current amount in accordance with the power supply potential will be fed from each power supply.[0158]
• In the configuration shown in FIG. 6, if there is any difference between the DC voltage output from[0159]power supply150 and the DC voltage output frompower supply160, the power supply current is fed only from the satellite broadcast receiver connected to one port.
• On the contrary, the current amount in accordance with the power supply potential is fed from each power supply with the use of[0160]current distribution circuit170 as shown in FIG. 8, so that the excessive current borne by the satellite broadcast receiver connected to LNB can be prevented.
• (Fifth Embodiment)[0161]
• FIG. 9 is a diagram illustrating a power supply circuit and[0162]periphery portion6 for use in LNB in accordance with a fifth embodiment.
• In the configuration shown in FIG. 9, switch[0163]IC190 directly outputs power supply potential BIAS1 to be provided toLNA22A and power supply potential BIAS2 to be provided toLNA22B. In other words,power supply circuit40 and block39 shown in FIG. 2 are integrated in an IC and accommodated in one package. This can further reduce the entire LNB in size.
• (Sixth Embodiment)[0164]
• FIG. 10 is a diagram illustrating a power supply circuit and periphery portion[0165]7 in accordance with a sixth embodiment.
• The power supply circuit and periphery portion[0166]7 has a similar configuration as the power supply circuit andperiphery portion5 shown in FIG. 7.Block39B receives IF signals R1A and L1A fromLNA22A amplifying a signal from a first satellite, and IF signals R2A and L2A fromLNA22B amplifying a signal from a second satellite.
• Meanwhile, block[0167]39C receives IF signals R3A and L3A fromLNA22C amplifying a signal from a third satellite, and IF signals R4A and L4A fromLNA22D amplifying a signal from a fourth satellite.
• Power supply potential BIAS[0168]1 fed fromswitch circuit52A is then provided toLNA22A and LNA22C. Power supply potential BIAS2 output fromswitch circuit54A is provided toLNA22B andLNA22D.
• Because of such a configuration, for example when a satellite broadcast receiver connected to port PO[0169]1 selects the first satellite and a satellite broadcast receiver connected to port PO2 selects the third satellite, the supply of power supply potential BIAS2 toLNA22B andLNA22D is stopped, thereby reducing the power consumption of LNB as a whole.
• As described above, in accordance with the present invention, it is possible to reduce the power consumption necessary to amplify a broadcasting signal from an unselected satellite in LNB that receives signals from a plurality of satellites. Therefore, even a satellite broadcast receiver with a limited current-supply capability can be connected.[0170]
• Furthermore, since a signal is selected by the switch, the noise level of the received signal is reduced.[0171]
• Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.[0172]

Claims (8)

What is claimed is:

1. A satellite broadcast receiving converter allowing a first satellite broadcast receiver to receive broadcasting signals transmitted from a plurality of satellites, comprising:

a first signal receiving portion receiving a first broadcasting signal transmitted from a first satellite of said plurality of satellites to supply a first RF signal;

a first amplifying portion amplifying said first RF signal;

a second signal receiving portion receiving a second broadcasting signal transmitted from a second satellite of said plurality of satellites to supply a second RF signal;

a second amplifying portion amplifying said second RF signal;

a first frequency conversion portion converting outputs of said first and second amplifying portions respectively to first and second IF signals in an intermediate frequency band, selecting and outputting one of said first and second IF signals;

a third amplifying portion amplifying an output of said first frequency conversion portion;

a first port receiving a signal from said third amplifying portion for output to said first satellite broadcast receiver;

a first DC component blocking portion provided between said third amplifying portion and said first port;

a power supply circuit receiving a first external power supply potential from said first satellite broadcast receiver through said first port and independently supplying first and second internal power supply potentials respectively to said first and second amplifying portions; and

a control portion instructing inactivation of an internal power supply potential, corresponding to an unselected satellite, of said first internal power supply potential and said second power supply potential to said power supply circuit in accordance with a select instruction applied from said first satellite broadcast receiver, and performing select control of said first frequency conversion portion.

2. The satellite broadcast receiving converter according toclaim 1, wherein

said power supply circuit includes

a power supply potential generation portion receiving said first external power supply potential,

a first switch circuit rendered conductive in accordance with an output of said control portion for outputting an output of said power supply potential generation portion as said first internal power supply potential, and

a second switch circuit rendered conductive complementarily to said first switch circuit for outputting the output of said power supply potential generation portion as said second internal power supply potential.

3. The satellite broadcast receiving converter according toclaim 1, further comprising:

a fourth amplifying portion amplifying an output of said first frequency conversion portion;

a second port receiving a signal from said fourth amplifying portion for output to a second satellite broadcast receiver; and

a second DC component blocking portion provided between said fourth amplifying portion and said second port, wherein

said first frequency conversion portion selects and outputs one of said first and second IF signals to said third amplifying portion in accordance with an output of said control portion, and selects and outputs one of said first and second IF signals to said fourth amplifying portion independently of selection for said third amplifying portion,

said control portion including

a first detection portion detecting an instruction from said first satellite broadcast receiver and

a second detection portion detecting an instruction from said second satellite broadcast receiver,

said power supply circuit including

a power supply potential generation portion receiving said first external power supply potential and a second external power supply potential provided from said second satellite broadcast receiver through said second port,

a first switch circuit rendered conductive in accordance with an output of said first detection portion and an output of said second detection portion for outputting an output of said power supply potential generation portion as said first internal power supply potential, and

a second switch circuit rendered conductive in accordance with the output of said first detection portion and the output of said second detection portion for outputting the output of said power supply potential generation portion as said second internal power supply potential.

4. The satellite broadcast receiving converter according toclaim 3, wherein

said first switch circuit is rendered conductive when at least one of the output of said first detection portion and the output of said second detection portion indicates selection of said first satellite, and is rendered non-conductive when neither of the output of said first detection portion and the output of said second detection portion indicates selection of said first satellite, and

said second switch circuit is rendered conductive when at least one of the output of said first detection portion and the output of said second detection portion indicates selection of said second satellite, and is rendered non-conductive when neither of the output of said first detection portion and the output of said second detection portion indicates selection of said second satellite.

5. The satellite broadcast receiving converter according toclaim 3, wherein

the instruction from said first satellite broadcast receiver to said first detection portion is provided through said first port as the presence or absence of a first pulse signal combined with said first external power supply potential,

the instruction from said second satellite broadcast receiver to said second detection portion is provided through said second port as the presence or absence of a second pulse signal combined with said second external power supply potential, and

both of said first and second pulse signals are signals indicative of selection of said first satellite,

said power supply circuit further including

a first sense circuit sensing that said first external power supply potential is fed from said first satellite broadcast receiver to said first port, and

a second sense circuit sensing that said second external power supply potential is fed from said second satellite broadcast receiver to said second port, wherein

said second switch circuit is rendered conductive in a first case where said first detection portion does not detect said first pulse signal and said first sense circuit senses that said first external power supply potential is fed and in a second case where said second detection portion does not detect said second pulse signal and said second sense circuit senses that said second external power supply potential is fed, and said second switch circuit is rendered non-conductive in other cases.

6. The satellite broadcast receiving converter according toclaim 3, wherein

said power supply circuit further includes a current distribution circuit receiving said first and second external power supply potentials respectively from said first and second ports and supplying operating power supply current to said power supply potential generation portion while preventing an unbalanced current supply from one of said first and second satellite broadcast receivers.

7. The satellite broadcast receiving converter according toclaim 1, wherein

said control portion and said power supply circuit are accommodated in one IC package.

8. The satellite broadcast receiving converter according toclaim 1, further comprising:

a fourth amplifying portion receiving said first internal power supply potential as an operating power supply potential and amplifying a third RF signal receiving a third broadcasting signal transmitted from a third satellite of said plurality of satellites;

a fifth amplifying portion receiving said second internal power supply potential as an operating power supply potential and amplifying a fourth RF signal receiving a fourth broadcasting signal transmitted from a fourth satellite of said plurality of satellites;

a second frequency conversion portion converting outputs of said third and fourth amplifying portions respectively to third and fourth IF signals in an intermediate frequency band, selecting and outputting one of said third and fourth IF signals;

a sixth amplifying portion amplifying an output of said second frequency conversion portion;

a second port receiving a signal from said sixth amplifying portion for output to a second satellite broadcast receiver; and

a second DC component blocking portion provided between said sixth amplifying portion and said second port,

said control portion including

a first detection portion detecting an instruction from said first satellite broadcast receiver and

a second detection portion detecting an instruction from said second satellite broadcast receiver,

said power supply circuit including

a power supply potential generation portion receiving said first external power supply potential and a second external power supply potential provided from said second satellite broadcast receiver through said second port,

a first switch circuit rendered conductive in accordance with an output of said first detection portion and an output of said second detection portion for outputting an output of said power supply potential generation portion as said first internal power supply potential, and

a second switch circuit rendered conductive in accordance with the output of said first detection portion and the output of said second detection portion for outputting the output of said power supply potential generation portion as said second internal power supply potential.

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